Abstract

Recent experimental and theoretical studies suggest that biological photosynthetic complexes utilize the quantum coherence
in a positive manner for efficient and robust flow of electronic excitation energy. Clear and quantitative understanding of
such suggestion is important for identifying the design principles behind efficient flow of excitons coherently delocalized
over multiple chromophores in condensed environments. Adaptation of such principles for synthetic macromolecular systems has
also significant implication for the development of novel photovoltaic systems. Advanced theories of resonance energy transfer
are presented, which can address these issues. Applications to photosynthetic light harvesting complex systems and organic
materials demonstrate the capabilities of new theoretical approaches and future challenges.

Images

Figure 1.

The arrangement of chromophores in the LH2 of Rps. Acidophila (left figure) and the energy level diagram of a typical B850 exciton band (right figure). In this diagram, solid red lines represent major bright states and dashed red lines represent weakly bright states.

Spectral lineshape calculated for an ensemble of the B800 rings from Rps. acidophila including static disorder and quantum coherence effect.122 We compare the simulated spectrum (solid line) with the experimental absorption spectrum at 6 K (open circle). A Gaussian fit to the red side of the simulated spectrum (dashed line) is also presented to show that the long tail at the blue side of the band cannot be explained by a Gaussian inhomogeneous lineshape.

A comparison of the distributions of the average B800 → B850 RET rate predicted by a B800 dimer model and a B800 monomer model. The theoretical B800 → B850 RET rate at kBT = 10 cm−1 is calculated from the MC‐FRET theory. The insert is a schematic of RET pathways in the B800 dimer model, showing alternative pathways when the coherence enables rapid energy transfer between the two B800 states.

Arrangement of bacteriochlorophylls (PM, PL, BM, and BL) and bacteriopheophytins (HM and HL) in the RC from the purple bacterium Rb. sphaeroides, and the experimental linear absorption spectrum measured at 77 K.

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